Experimental Study On Flexural Behavior Of Stone Beams Strengthened By CFRP Sheets

The stone buildings have strong architectural features and long histories. There are still numerous stone buildings existing in many areas of China, especially in the southeast region of Fujian Province. Flexural members like stone beams will collapse once a crack occurs at the tension side. In order to improve the safety of the stone buildings, it is necessary to develop an economic and reasonable method for strengthening stone beams. A technique for strengthening stone beams using carbon fiber-reinforced polymer(CFRP) sheets was proposed in this dissertation. Two series of tests were performed to study the bond behavior of the interface between the stone and CFRP sheets and the flexural behavior of stone beams strengthened by CFRP sheets.Thirty single shear tests were carried out to study the bond behavior of the interface. The test parameters included the bond length, number of CFRP layers and the roughness of the stone surface. The failure modes of the specimens included the failure between the primer and CFRP sheets, the damage of stone under the bonding interface, and the stone cracking near the loading side-end. The test results indicate that there exists an effective bond length between CFRP sheets and stone. After the actual bond length exceeds the effective bond length, the peak load no longer increases as the actual bond length increases. The number of CFRP layers has little effect on the effective bond length between CFRP sheets and stone. The effective bond length decreases as the roughness of stone surface increases. When the actual bond length is large enough, the roughness of stone surface shows little influence on the peak load. Based on the test results, a bond-slip constitutive model was proposed for the interface between CFRP sheets and stone.Flexural testes were carried out on eight stone beams to study the influence of the roughness of the bond surface, the CFRP amount and the additional anchorage methods on the flexural behavior of the strengthened beams. The additional anchorage methods included the U-strips of CFRP, groove on the bond surface and end anchorage. The bare stone beams ruptured at a small deflection and exhibited a brittle failure phenomenon. The strengthed beams exhibited a more ductile failure phenomenon that can still sustained some loads after cracking. The cracking load was increased by 10% to 28% after the stone beam was strengthened by CFRP sheets. The CFRP amount has little effect on the cracking load, but the load-carrying capacity of strengthened stone beams increases as the CFRP amount increases. Grooving on the bond surface cannot effectively prevent the debonding failure.The failure modes of the strengthened beams with ordinary paste or groove is debonding. The roughness of the bond surface has little influence on the maximum load-carrying capacity after cracking, but grooving on the bond surface can significantly improve the maximum load-carrying capacity after cracking. The strengthened beams with U-strips or the end anchorage had a residual load-carrying capacity after all the CFRP debonded, which increases the effectiveness of the material. The proposed CFRP strengthening method is effective in improving the load-carrying capacity and ductility of the stone beams.The failure process of the stone beams strengthened by CFRP sheets can be divided into three stages, namely elastic stage, debonding stage and hardening stage. The specimens with ordinary paste or groove did not have the hardening stage. Based on the test results and plane section assumption, formulas for calculating the cracking load of strengthened stone beams were proposed. The calculated results are in good agreement with the test results.